The line of mud pasted onto ones back, after one has been riding a bike through said mud, thus producing the upward lift of said mud, from the circular motion of the wheels on said bike in motion.
Said word was created after observation of competative bikers training in the rain who stopped at a diner and all looked like skunks with their enormus examples of back-splatter in its perfect state.

"woah! those competative bikers who have been training in the rain have totally perfect back-splatter!"...."no doubt if they had been doing that naked they would resemble the negative images of skunks!"

Noun. The high-velocity pattern made by liquid fecal matter on the back of the toilet above the waterline. This pattern is formed when one has an uncontrolled evacuation of the bowels as he or she is in the process of sitting down and is still in a leaning-forward position. Because the movement associated with this phenomenon is usually time-consuming, the resulting back-splatter typically dries and will not come off when the toilet if flushed. Back-splatter usually lasts until physically removed with a brush and Comet.

Man, I know Al has been in here today, there's already back-splatter on the toilet.